Every year between autumn and spring, Venice and the neighboring costal town of Chioggia suffers from bouts of temporary flooding caused by exceptionally high tides that occur in the northern Adriatic Sea. The flooding is periodic, just like any high tides, and they reach their maximum in the Venetian Lagoon where they cause partial flooding of Venice and Chioggia. The phenomenon is locally known as acqua alta.
Acqua alta occurs when high tides caused by the moon's gravitational pull coincide with a strong scirocco, a warm wind blowing across the Mediterranean that forces water from the Adriatic into the Venetian lagoon. This coincidence happens from about the middle of October to the beginning of December. Since, acqua alta is a tidal phenomenon, it lasts three to four hours, during high tide. Once water goes down again, things go back to normality. The water may last a bit longer if there is a particularly strong scirocco, but is assured to drain away when the tide subsides, which happens every six hours.
The flooding caused by the acqua alta is not uniform throughout the city of Venice. A city-commissioned study showed, a tide up to 90 cm. above sea level leaves Venice virtually unaffected, while 50 cm. of additional water hit more than a third of the city.
Since acqua alta depends upon a confluence of weather and tides, it is predictable at least a couple of days before it happens. The municipality runs a service notifying residents of the potential danger. To allow pedestrian circulation during floods, the city installs a network of gangways (wide wood planks on iron supports) reproducing the main urban paths. This gangway system is generally set at 120 cm above the conventional sea level, which can result in partial or complete flooding when higher tides occur.
Acqua alta causes very limited inconvenience to Venetians and tourists. In these cases, the only thing to do is to be patient and wait a few hours for the following ebb. Otherwise, grabbing a pair of cheap rubber boots is recommended.
Subscribe to our Newsletter and get articles like this delivered straight to your inbox